BASICS OF AN INSTRUMENT AIR SUPPLY SYSTEM
Introduction The air used must be cleaned, dry and oil-free to ensure that small lines, restrictions and nozzles will not be plugged by dirt, oil...
Category : Process Control
what is cascade control?
A simple control system drawn in block diagram form looks like this: Information from the measuring device (e.g. transmitter) goes to the controller, then to...
BASICS OF ON/OFF CONTROLLER
Introduction In control theory, an on/off controller, also known as a hysteresis controller, is a feedback controller that switches abruptly between two states. These controllers...
Calibration of control valve positioner
Introduction Positioner is a device put into a valve to ensure that it is at correct position.An open/close operation of control valve also can be...
Basics of PID controller (Proportional – Integral – Derivative)
PID (Proportional – Integral – Derivative ) Controller Proportional The proportional term makes the current error signal multiplied with a gain (Kp).The result will be...
Override Control
Override It is sometimes necessary to limit a variable in order to maintain safe operation or protect process equipment. If this variable is a function...
Feedforward Control System
Feedforward A Feedforward control system measures a disturbance in variable, predicts its effect on the process and applies corrective action. Given an exact model of...
Cascade Control System
Cascade In cascade control system two controllers are cascaded to each other as shown in the diagram below. Primary controllers output is fed to...
Ratio Control
Ratio Control In Ratio Control, the controlled variable is the ratio of two measured variables. Control is effected by adjusting one of the variables –...
Common Control Loops
Common Control Loop 1.Flow Liquid flow processes are fast, typically 0.5 sec response or less. Gas flow is slightly slower because of the...